Silicon interposer wires above 3 mm typically exhibit some degree of inductive behavior. Current through a wire induces a magnetic field across adjacent wires and introduces inductive noise. Return current paths may be provided for optimal signal integrity. In single-ended signaling, the worst-case scenario is when all bits of a bus flip in the same clock cycle. One way to provide a return current path is to use differential signaling. A pair of wires are used for every symbol to be transmitted. For instance, in non-return-to-zero (“NRZ”) differential signaling, to transmit a logic 1, one wire is at a high-voltage level while the other is at ground. To transmit a logic 0, the two wires swap voltage values. As a result, any signal transition results in equal and opposite currents on the two wires. NRZ differential signaling is currently used on printed circuit boards (“PCBs”) for high-speed signaling with serializers-deserializers (“SERDES”). While differential signaling is effective in providing return current paths, the wiring over head is 100% since every bit requires two wires to transmit.
It would be useful to provide less digital noise with less overhead than differential signaling.